Wide bandgap semiconductors such as GaN, SiC, and diamond have excellent material properties for a material as a semiconductor device, such as a breakdown voltage, electron mobility, and heat conductivity in comparison with Si. Recently, research and development have been eagerly ongoing to obtain commercially available products. In particular, a high electron mobility transistor (HEMT) structure having a hetero-junction channel such as AlGaN/GaN has a high electron mobility and a high carrier density. For this reason, the GaN device has advantages such as an excellent high-frequency characteristic or a low on-resistance in comparison with the Si device and has been expected as the next-generation switching device in the field of the power electronics.
However, the GaN device having a typical AlGaN/GaN hetero-junction channel is a normally-on type in which a gate threshold voltage is negative, and the gate electrode may be easily broken down when an excessive positive voltage is applied thereto. In order to avoid such a phenomenon, a diode for clipping a gate voltage to protect the gate electrode is generally installed between the gate and the source outside the chip. As a result, the number of components in a circuit may increase, and wiring on the circuit board may become complicated.